# Anthropogenic Underwater Noise Induces Anxiety-like Behavior in Zebrafish

## TL;DR

Underwater noise from human activities causes anxiety-like behavior in zebrafish, especially at night, by disrupting stress and brain chemical systems.

## Contribution

This study reveals that anthropogenic noise disrupts neuroendocrine pathways in zebrafish, with sex-specific and time-of-day effects.

## Key findings

- Noise exposure increased bottom-dwelling and reduced exploration in zebrafish, especially at night.
- Nighttime noise elevated cortisol and altered serotonin and dopamine levels in zebrafish brains.
- Disruptions in 5-HT and DA pathways were observed, with sex-specific differences in response.

## Abstract

Anthropogenic underwater noise is an emerging environmental pollutant, yet its impacts on fish remain poorly understood. This study examined the effects of continuous daytime and nighttime noise exposure on adult zebrafish. We found that noise triggered anxiety-like responses, including increased bottom-dwelling and reduced exploration, with more pronounced effects during the night. Physiological and molecular analyses revealed that these behavioral changes were linked to a dysregulated stress hormone response and altered levels of key neurotransmitters in the brain, specifically serotonin and dopamine. Our findings demonstrate that underwater noise pollution can adversely affect fish welfare by disrupting core neuroendocrine pathways. This evidence is crucial for informing environmental policies aimed at mitigating the ecological impacts of anthropogenic noise.

Underwater noise pollution, driven by human activities, is an emerging environmental concern, yet its effects on fish behavior and physiology remain poorly understood. As a vertebrate model with conserved stress pathways, zebrafish (Danio rerio) is well-suited for investigating the mechanistic basis of such impacts. We hypothesized that daytime and nighttime noise exposure would differentially induce anxiety-like behavior and associated neuroendocrine disruptions in zebrafish, with effects varying by sex. To evaluate this hypothesis, adult zebrafish were exposed to anthropogenic noise (100–1000 Hz, 130 dB) for seven days, specifically during daytime (08:00–20:00) and nighttime (20:00–08:00) periods. Behavioral assays revealed that noise exposure delayed the first entry of females into the top zone during daytime, while both sexes exhibited prolonged bottom-dwelling and reduced exploratory behavior under nighttime noise. Physiological analyses showed elevated plasma cortisol levels in females, accompanied by up-regulated HPI-axis genes, whereas males displayed a non-significant cortisol increase. Neurotransmitter profiling indicated a sex-specific response to nighttime noise: In females, brain 5-hydroxytryptamine (5-HT) showed a non-significant increasing trend, whereas in males it was significantly elevated, while dopamine (DA) decreased in both sexes. Gene expression analysis further revealed disruptions in 5-HT and DA pathways. These findings demonstrate that underwater noise induces anxiety-like behavior in zebrafish by dysregulating endocrine and neurotransmitter systems, with nighttime noise exhibiting more pronounced effects, suggesting that chronic exposure to anthropogenic noise may impair natural behavior and stress regulation in aquatic species, particularly during nighttime periods.